oxides in weld (macro)

Date 10-11-2007 17:57

Hi Hogan, what I have learned in the past is that gmaw and fcaw don't mix to good.There are others on this forum that can tell you the reason why they don't better than I can.
Milton

By hogan

Date 10-11-2007 18:11

thanks for the reply milton. this connection has been made this way for years. it was just reasontly that this issue came up

By js55

Date 10-11-2007 18:16

First of all I would ask;
What is the joint configuration?
What are the materials?
Where were the macros taken from?
Are you sure they're oxides?
Did you macro unaffected BM?
How did you segregate the processes for macro?

By hogan

Date 10-11-2007 18:26

joint: B-U2a-GF
material: A36
macros only able to be taken from end 2" of 20' weld
the testing lab is calling them oxides
you can see no indications in the b.m. on the macros
i'm not sure i understand your last question
in weld 4 you can see the fcaw tack on the btm righthand side. the remainder of the root is gmaw

By 803056

Date 10-11-2007 21:16

I would question their laboratory technique. These do not look like normal macros of welds in the as welded condition on carbon steel. There is no obvious heat affect zone or other characteristics of a typical weld.

Al

By hogan

Date 10-11-2007 21:56

sorry, poor choice of words. the samples were not etched. only polished and magnified.

By CWI555

Date 10-12-2007 02:05

I hate to the master of the obvious here, but if your joints have been done the same way for years with the same fillers for an equal number of years with no problem, Then your only other variable is something new. Without a proper etch and magnification I can't tell much from the pictures, but it seems to me since since all three processes are experiencing the same problem in greater or lesser degrees, the only thing left would be the base material. Suggest cutting three grooves into a single plate of that material spaced enough to avoid interactions of HAZ and running SAW, FCAW, and GMAW in them then cutting and proper macro. If it's the base material, it will be in all three. If it was one or the other processes it would only show up in that process.

My two cents worth,
Gerald

By hogan

Date 10-12-2007 13:17

i had tensils and chemestry tests performed on the base metal. everything looked good and matched the origonal mtr.

By js55

Date 10-12-2007 13:30

hogan,
Unless I'm looking at the macros wrong, it appears to me there are 'oxides' in the backing bar.
Don't the photos show oxides below the joint members gap?

By hogan

Date 10-12-2007 13:57

js55,
i noticed that also, but was wondering if that could be diluted through 3/4" to the top of the weld

By js55

Date 10-12-2007 14:23

Most assuredly. And, they may not all be oxides. They could be compounds of S, P, and Si as well. If the backing bar material is high in these elements (we are talking A36 here) they could actually be in solid solution to a great extent in the BM (and therefore invisible to etching) and then form compounds with the deoxidizers and fluxing agents of your SAW flux and FCAW wire and become etch visible in the weld metal and fusion zone. Also, keep inmind high Mn in FCAW wires and the possbility of forming MnS if the S is high in the A36.

By CWI555

Date 10-12-2007 13:35

Don't know what to tell you then. Before it's good, now it's not. Something had to change. It can't be gas, as one of those processes doesn't use it, It's not likely the wire, as you have to have a different one for the FCAW. Removing the the fillers from the equation, and assuming as you've stated that it's not been a problem before, there isn't much left it could be. Something would just about have to be in the base materials.

By 803056

Date 10-12-2007 22:30

I wouldn't get overly excited until the samples were properly prepared and etched.

It's difficult if not impossible to see how many weld passes are involved or where the "oxides" are located. The level of magnification of the macro-etch should be on the order of 10X in which case the "oxides" may not be visible and of no consequence.

Most welds are going to contain oxides visible at some level of magnification and I wouldn't expect them to appear in the photomicrograph to be the same or in the same concentration as in the base metal. One reason for the difference is the orientation of the grain boundaries in the weld versus the base metal. The density of the "inclusions" appear to be consistent for all the welding conditions shown in the photomicrographs. If there was something wrong with one of the processes, there would be more pronounced differences in the occurance and density of the "inclusions".

Best regards - Al